1. Field of the Invention
The present invention relates to a technology for driving a display panel composed of a set of cells that are display elements possessing a memory function. More particularly, this invention is concerned with a device for displaying an image on an alternating current (AC) type plasma display panel (PDP) with interlaced scanning.
2. Description of the Related Art
In the AC type PDP, a voltage waveform is applied alternately to two sustaining electrodes in order to sustain discharge and emit light for display. One discharge is completed in one to several microseconds immediately after application of a pulse. Positively charged ions stemming from the discharge are accumulated on the surface of an insulating layer over electrodes to which a negative voltage has been applied. Likewise, electrons carrying negative charges are accumulated on the surface of the insulating layer over electrodes to which a positive voltage has been applied.
First, discharge is initiated with a pulse (writing pulse) of a high voltage (writing voltage) in order to produce a wall charge. Thereafter, a pulse (sustaining discharge pulse) of a voltage (sustaining discharge voltage) lower than the previous voltage is applied. The previously accumulated wall charge is then added to the voltage. The voltage becomes high relative to the potential in the discharge space, and exceeds the threshold of a discharge voltage. Consequently, discharge is started. In other words, once a display cell is discharged for writing, when sustaining discharge pulses of opposite polarities are applied alternately, the display cell in which a wall charge has been produced sustains discharge. This property of a display cell is referred to as a memory effect or memory function. In general, the AC type PDP utilizes the memory effect to carry out display.
In an AC type PDP of a prior art, X electrodes that are one group of sustaining electrodes and Y electrodes that are the other group thereof are arranged alternately. Discharge is initiated in regions defined between odd-numbered X electrodes and odd-numbered Y electrodes, and in regions defined between even-numbered X electrodes and even-numbered Y electrodes. In other words, display cells are defined between odd-numbered X electrodes and odd-numbered Y electrodes, and between even-numbered X electrodes and even-numbered Y electrodes. No display cells are defined between odd-numbered Y electrodes and even-numbered X electrodes, and between odd-numbered X electrodes and even-numbered Y electrodes. However, this poses a problem that it is hard to attain high definition and high luminance. The present inventor has disclosed a PDP in Japanese Unexamined Patent Publication No. 9-160525. In the PDP, for interlaced scanning, display cells are defined even between an odd-numbered Y electrodes and even-numbered X electrodes, and between odd-numbered X electrodes and even-numbered Y electrodes, and thus high definition and high luminance are attained. The present invention is adapted to a plasma display panel (PDP) in which, as in the one disclosed in the Japanese Unexamined Patent Publication No. 9-160525, discharge is initiated in regions defined between a Y electrode and X electrodes across the Y electrode in order to specify display cells.
In the PDP disclosed in the Japanese Unexamined Patent Publication No. 9-160525, after a second-half addressing period is completed, all X electrodes and Y electrodes are temporarily set to zero level. Thereafter, sustaining discharge pulses that are mutually out of phase are applied alternately to adjoining slits coincident with lines to be displayed. At this time, depending on which of the sustaining discharge pulses of opposite polarities are applied at the start of a sustaining discharge period, it is determined in which of odd-numbered ones and even-numbered ones of odd display slits coincident with lines to be displayed sustaining discharges should be initiated first. The start of sustaining discharge is delayed in the other ones of the odd display slits. The same applies to even display slits.
The luminance of a PDP depends on the frequency of sustaining discharge. For realizing a high-luminance PDP, the cycle of a sustaining discharge pulse must be short. However, as mentioned above, if an initial sustaining discharge is largely delayed, before the initial sustaining discharge is completed, the polarity of a sustaining discharge pulse is reversed. When this occurs, movement of charges between an X electrode and Y electrode deriving from sustaining discharge is not sufficiently achieved. There is a fear that subsequent sustaining discharge may not be carried out. Consequently, a normal display fails.
Moreover, the polarity of a sustaining discharge pulse applied to adjacent odd discharge slits at the time of initial sustaining discharge is opposite to that of an accumulated wall charge. A discharge occurring in an odd-numbered odd display slit will not affect a wall charge in an even-numbered odd display slit. However, when the second sustaining discharge occurs in the odd-numbered odd display slit at time instant, the polarity of a sustaining discharge pulse applied to the even-numbered odd display slit has already been reversed. Moreover, occurrence of initial sustaining discharge in the even-numbered odd display slit is delayed. This poses a problem that the wall charge in the even-numbered odd display slit disappears because of the second sustaining discharge occurring in the odd-numbered odd display slit in the meantime. When the disappearance of a wall charge occurs, sustaining discharge is not carried out. Consequently, a normal display fails.
Furthermore, during the sustaining discharge period, there is a difference of one time between the number of glows in a slit to be addressed during the first-half addressing period and the number of glows in a slit to be addressed during the second-half addressing period. The number of glows within a sub-field that is weighted a little is several times. Even the difference of one time therefore leads to a problem on gray-scale display.
Moreover, there is a problem that erase to be carried out at an erasing step succeeding the sustaining discharge period is achieved imperfectly depending on the magnitude or polarity of a charge on an electrode.